Please manually change the languages and gender to your unsupported combination, for example languages="en:zh zh:zh" gender = "female"
An onvoicefailure must be reported since no voice can match the required languages and gender.
Meanwhile, since the value for onvoicefailure attribute is "keepexisting",
the synthesis processor must not change the voice.
Here is an example,
(1) Your engine have only two voices
1. one male voice can speak English with Chinese accent and can speak Chinese with Chinese accent
2. one female voice can only speak Chinese with Chinese accent.
(2) In the first voice element, the male voice will be selected.
(3) In the second voice element, an onvoicefailure must be reported since no voice can match the required languages and gender.
(4) since the value for onvoicefailure attribute is "keepexisting", the male voice will continue to be used in the second voice element.
I want to say
I can not find such a voice.